The attachment of multiple ubiquitin (Ub) moieties to a protein is referred to as polyubiquitination, and serves as a signaling mechanism for degradation of the selected protein. The rate of protein degradation is altered in cases of alcoholic liver disease, and the objective of this research proposal is to investigate the effects of pathological concentrations of 4-hydroxynonenal (4-HNE) on the polyubiquitination of intracellular hepatocyte proteins. This particular aldehyde has been selected due to its implication in multiple pathologies (e.g. atherosclerosis and reperfusion injury) through its ability to covalently modify proteins. The experiments proposed within have been designed to test the general working hypothesis that 4-HNE modulates the rate of protein polyubiquitination through direct modification of the substrate protein. The first phase of this research plan entails the selection of model proteins for investigating protein polyubiquitination in an in vitro system, and the effect of adduct formation between these proteins and 4- HNE on this process. The foundation provided by these early experiments will allow for the characterization of 4-HNE adducts formed with the model proteins, followed by the identification of ubiquitin-binding sites and the respective interaction of 4-HNE with these sites. Finally, the balance between ubiquitination and deubiquitination as influenced by 4-HNE will be assessed. When complete, the data provided by this research will provide further insight into the mechanisms by which 4-HNE exerts toxicity. [unreadable] [unreadable]